The invention relates generally to automatically controllable fluid flow control dampers and more particularly to a low pressure fluid operated fluid flow control damper assembly particularly useful in HVAC systems.
Fluid flow control dampers are used in a wide variety of applications, including heating, ventilation and air conditioning (xe2x80x9cHVACxe2x80x9d) systems to control the supply of conditioned air to various rooms or zones within a building. Damper assemblies commonly have been employed at room registers to control the flow of air into a room. These dampers typically include a pivotally mounted damper vane on the duct side of the register and an actuator lever which protrudes on the room side of the register for enabling manual adjustment of the damper vane.
An exemplary damper device is a mechanical damper assembly that includes a short piece or section of duct that can be spliced into a system of air ducts. The damper assembly further includes a damper vane generally inside the duct, pivotally mounted to a shaft for rotation between open and closed positions. The damper assembly also may include a motor that is mounted to the outside of the duct and connected to the vane shaft through the duct wall for automating control of the damper vane.
The aforesaid type of mechanical damper assembly is somewhat difficult to install in an existing duct, however. In order to splice the damper assembly the installer has to cut a length from the existing duct. This often requires that the installer dismantle the existing duct to enable such cutting and/or to assemble the damper assembly between adjacent sections of the existing duct. This dismantling, cutting and reassembly of the ductwork is time-consuming and expensive.
Reference may be had, for example, to U.S. Pat. No. 5,458,148 which discloses an improved damper assembly and installation method for mounting a damper assembly in an existing duct system. In this embodiment, the damper assembly includes a support base for externally mounting to a side of an existing duct, and a damper vane mounted to the support base for movement between open and closed positions. An access opening is cut in the existing duct for insertion of the damper vane. The damper vane is located inwardly of the inner side of the support base so as to be positioned interiorly of the duct when the support base is mounted to the duct. A pneumatic actuator is mounted to an outer side of the support base and is operatively connected to the damper vane by a linkage for moving the damper vane between the open and closed positions. The support base also closes the access opening in the side wall of the duct.
While each of these damper assemblies has served its purpose and may continue to do so, they are not without disadvantages. Applicant has recognized that it would be desirable to provide a lower profile damper assembly that would be automatically controllable and would be readily installed in new or existing ductwork.
The present invention provides a novel damper assembly for fluid flow control that overcomes drawbacks associated with and/or improves upon prior art damper assemblies. More particularly, the present invention provides a low profile damper assembly that is compact and relatively easy to install inside new or existing ducts, including in situations where the outside surface of the duct is inaccessible.
An exemplary damper assembly provided by the present invention includes a damper vane and an electric actuator or a pneumatic piston-cylinder actuator connected to the damper vane for moving the damper vane between an open position and a closed position. The piston-cylinder actuator includes a piston and a cylinder that have cooperating nonelastomeric sliding sealing surfaces which provide essentially friction-free axial movement of the piston relative to the cylinder. The surfaces at the sliding interface between the piston and the cylinder preferably are smooth and function to provide a substantially air tight seal, thereby eliminating the need for elastomeric seals that normally would introduce additional friction into the actuator.
The piston and/or the cylinder are formed of a material selected from the group including metal, powdered metal, resin, glass, and polymer. The piston and/or the cylinder also may have a friction-reducing coating on the sealing surface thereof. Preferably, the piston-cylinder actuator has a powder-metal piston and a glass cylinder.
The resulting damper assembly is considerably smaller than previous motive devices. The damper assembly can further include a base, to which the damper vane and the piston-cylinder actuator are mounted, preferably on the same side of the base. The actuator can be controllably connected to a pneumatic control system through a fitting at one end of the cylinder, and the fitting has a threaded portion for mounting the actuator with respect to the base. The base may be configured for mounting to the exterior of a duct, in which case the piston-cylinder actuator may be mounted to the base such that a nipple portion of the actuator fitting is disposed at an exterior side of the base for connection to the pneumatic control system. The resulting damper assembly presents a minimal profile outside the damper vanes and can be installed inside the ductwork without unduly impeding airflow therethrough which is advantageous in shallow clearance situations, as well as providing an improved appearance.
The damper vane and the piston-cylinder actuator are interconnected by a drive rod. The drive rod is mounted to transfer substantially only axial forces from the actuator to the damper vane, for example, by using ball joints to connect the ends of the drive rod to the damper vane and the actuator piston. This arrangement prevents lateral or twisting forces from acting on the drive rod, which otherwise may cause the piston to bind in the cylinder. In addition, the actuator does not have to be precisely aligned with the damper vane, thereby facilitating manufacturing and installation.
The piston-cylinder actuator also may have a cylindrical cap that fits over an end of the cylinder to retain the piston in the cylinder. The cap has an oversized opening for passage of the drive rod therethrough. Particularly if the cylinder is made of glass, a substantially tubular protective boot may be used to substantially cover the outer circumferential surface of the cylinder. The boot preferably is made of an elastomer, such as rubber, to protect the cylinder, particularly prior to and during installation.
The damper vane also may include a plurality of damper vanes that cooperate to close a cross-section of a duct when the damper vanes are in closed positions, and a plurality of piston actuators. Each piston actuator is operatively connected to one of the damper vanes for opening and closing the damper vanes. The plurality of damper vanes may include a first damper vane that has an aperture, and a second damper vane that closes the aperture when both the first damper vane and the second damper vane are in their respective closed positions. The damper vanes lie in substantially parallel planes when both the damper vanes are in their open positions to present a minimal profile to the airflow. The plurality of damper vanes are used to supply different volumes of air through the damper assembly to mix fresh air with return air in varying proportions, to provide a varied amount of conditioned air according to varied requirements and/or to supply a constant but smaller amount of airflow until a greater or full amount of air supply is needed.
The damper assembly may include a spring connected to the damper vane for biasing the damper vane to a predetermined position. This feature is particularly advantageous in the event of a power failure to automatically open or close the damper vane under the action of the spring.
The invention also provides a damper assembly having a frame, a damper vane mounted to the frame for pivotal movement between open and closed positions, and an actuator for moving the damper vane between the open and closed positions. The frame has a cross-sectional shape that approximates or generally corresponds to a cross-sectional shape of a duct into which the damper assembly may be installed. The frame preferably has a gasket or elastomeric member disposed on the exterior thereof or positioned about at least a portion of its outer periphery to sealingly engage the frame with a duct wall. The actuator is located within the confines of a projection of the frame in an axial direction. Accordingly, the damper assembly may be inserted into an open end of a duct with the actuator disposed within the duct.
The present invention also provides a method of installing a damper assembly, the method including the steps of removing a register from an outlet of a duct, inserting the damper assembly into a duct adjacent the outlet, and replacing the register. Thus, the simple method provided by the present invention may be used to retrofit a building for automated damper control of the airflow where access to the ductwork is otherwise unavailable.
The present invention also provides a damper assembly having at least two duct wall-engaging members movable towards each other against a biasing force. The duct wall-engaging members preferably apply substantially equal forces against opposing walls of the duct to center and align the damper assembly in the duct. The duct wall-engaging members may apply unequal force against the duct wall to position the damper assembly off-center as well. The duct wall-engaging members include a leaf spring extending from lateral sides of the base, and at least one wall-engaging member having integral handle portions for easily grasping the damper assembly for insertion into a duct. Installation in a duct may be affected by retracting the duct wall-engaging members against the biasing force, inserting the damper assembly into the duct, and releasing the duct wall-engaging members so that the biasing force presses the duct-wall engaging members against the duct walls to hold, align and preferably center the damper assembly in a fixed location within the duct. A damper assembly having such wall-engaging members is particularly advantageous when the external surface of the duct is inaccessible, permitting the damper assembly to be installed from an end of the duct, perhaps with just one hand. Automatic self-centering is a particular advantage in a blind installation where the installer cannot easily see into the duct. By automatically centering the damper assembly, the present invention also minimizes the chance that rigid portions of the damper vane would scrape against the duct wall as the damper vane moves between its open and closed positions. The damper assembly is thus more likely than not to operate quietly.
The present invention also provides a damper assembly having a housing having a passage therethrough and a pair of doors mounted in the housing. The doors are movable between an open position where airflow through the passage is substantially free from interference by the doors, and a closed position where airflow through the passage is substantially zero. The damper assembly further includes an actuator assembly mounted in the housing to move the doors. The actuator assembly includes an actuator and a linkage interconnecting the doors such that movement of a piston portion of the actuator drives the movement of the doors between the open and closed positions. The linkage allows both doors to be driven by a common actuator.
The foregoing and other features of the invention are hereinafter fully described and particularly pointed out in the claims, the following description and annexed drawings setting forth in detail certain illustrative embodiments of the invention, these embodiments being indicative, however, of but a few of the various ways in which the principles of the invention may be employed.